When salt-containing water is diluted in fresh water, an extensive energy potential can be extracted. Salinity power is stable energy that is not reliant on weather or wind. It is renewable and does not generate any known serious environmental effects.
The principle of salinity power is called pressure-retarded osmosis (PRO), and refers to utilising the energy that can be released when salt water mixes with fresh water. This happens by carrying every chamber in a distinct vessel of a membrane. The membrane tolerates through-flow of fresh water, but not salt water, see FIG. 1. The fresh water will then flow through to the other side, and the energy in this flow can be tapped by using a turbine. The natural need for dilution of salt is so great that it corresponds to 27 bars, in other words five to six times the pressure in a water tap or to a downfall of 260 meters for fresh water. This power is the so-called osmotic pressure between fresh water and salt water.
Salinity power is one of the largest sources of renewable energy that is still not exploited. The exploitable potential world-wide is estimated to be 2000 TWh annually. Still considerable technological development is necessary to fully utilize this resource. Thus, the potential cost of energy from this source is still higher than most traditional hydropower, but is comparable to other forms of renewable energy that are already produced in full-scale plants.
For salinity power production, fouling and flow capacity of membranes are critical, and today the water membrane separating the two chambers, with seawater on one side and fresh water on the other side, respectively, is the limiting step in exporting the potential in salinity power production.
Since the discovery of the aquaporin water transport proteins are distinguished by their ability to selectively transport H2O molecules across biological membranes there has been a certain interest in devising an artificial water membrane incorporating these proteins, cf. published US Patent Application No. 2004/0049230 “Biomimetic membranes” which aims to describe how water transport proteins are embedded in a membrane to enable water purification. The preferred form described has the form of a conventional filter disk. To fabricate such a disk, a 5 nm thick monolayer of synthetic triblock copolymer and protein is deposited on the surface of a 25 mm commercial ultrafiltration disk using a Langmuir-Blodgett trough. The monolayer on the disk is then cross-linked using UV light to the polymer to increase its durability.
It has been suggested that a water purification technology could be created by expressing the aquaporin protein into lipid bilayer vesicles and cast these membranes on porous supports, cf. James R. Swartz, home page.
Furthermore, the present assignee has previously submitted an international patent application where aquaporins are comprised in a sandwich construction having either at least two permeable support layers separated by at least one lipid bilayer comprising functional aquaporin water channels or having a lipid bilayer surrounding a perforated hydrophobic support layer, cf. International patent application No. PCT/DK2006/000278, which claims the priorities of Danish patent application No. PA 2005 00740 and U.S. provisional patent application No. 60/683,466. The water channel comprising membranes disclosed in PCT/DK2006/000278 are incorporated by reference herein and are regarded as the most promising water membranes for use in the present invention and hence all disclosures in PCT/DK2006/000278 relating to water membranes and their preparation are regarded as important embodiments of the pre-sent invention.
All previously disclosed applications of using aquaporins in artificial membranes have been targeted at producing purified water. The present invention broadens the scope of using nature's water transporting channels, aquaporins, into the field of sustainable energy solutions.
The present invention aims at using biomimetic membranes comprising functional aquaporin channels to produce salinity power, using pressure retarded osmosis.